Tony Blair bodyguard left loaded gun in Starbucks when she went to the toilet

The officer visited the lavatory at a Starbucks in Central London and removed her holster, which held a Glock 17 semi-automatic.

After finishing in the toilet, she bought a coffee and left. The pistol lay on the floor for 20 minutes before a horrified member of staff saw it and called 999.

The Starbucks on Edgware Road where the bodyguard left her Glock pistol

Armed police raced to the premises in Edgware Road – near one of Mr Blair's homes – to recover the gun.

The officer, who a source said was 'among the top in her class during training', realised her mistake and retraced her steps, frantically searching for the gun. It was linked to her by checking the serial number.

The woman, who is in her thirties and plain-clothed, was immediately removed from operational duties with the elite SO1 Specialist Protection Command.

Mistake: Tony Blair's female bodyguard left a gun like the one above in the coffee shop toilet

The protection unit is responsible for the personal safety of senior politicians and VIPs including former prime ministers Mr Blair, now Middle East envoy, and Baroness Thatcher.

A source said: 'If a child or criminal had picked it up there could have been terrible consequences.

'This has come as a shock. The officer is inconsolable and seriously regrets her mistake.'

The source added: 'Everyone is fond of her. She was among the top in her class during training, but her firearms career could be over.'

A Scotland Yard spokesman said: 'A police-issue firearm was left unattended in a central London café on August 29 and was found by a member of the public.

'The weapon belongs to a Metropolitan Police authorised firearms officer who was on duty at the time.'

The Met's Directorate of Professional Standards is investigating.